Turkish authorities are examining motorway cameras in the search for a black van they believe carried the body of Jamal Khashoggi from the Saudi consulate in Istanbul last Tuesday – one of six cars investigators say belonged to a Saudi hit squad thought to be behind the suspected murder of the dissident journalist.

Officials say the convoy left the consulate around two hours after Khashoggi entered. Security camera footage shows boxes being loaded into the van, which carried diplomatic number plates.

After leaving the consulate grounds, three cars turned left on to a main road while the other three turned right.

Investigators say one of the vehicles, a van with blacked out windows, has become the focus of the investigation, and was briefly tracked to a nearby motorway.

Nearly a week since Khashoggi disappeared, Recep Tayyip Erdogan stepped up his calls for Riyadh to explain what happened to the high-profile critic of the Saudi leadership.

The Turkish president had struck a measured tone when pressed on Khashoggi, while allowing government officials and state media to drip-feed allegations. Details of the convoy were disclosed by the pro-government Daily Sabah newspaper.

“We have to get an outcome from this investigation as soon as possible,” Erdogan said from Budapest. “The consulate officials cannot save themselves by simply saying: ‘He has left’.”

He said he was personally following the case but had no new evidence to table.

Turkish Foreign Ministry’s spokesman, Hami Aksoy, said on Tuesday Saudi authorities have notified Ankara they were “open to cooperation” and would allow the consulate building to be searched. The ministry did not say when it would happen.

At the same time, the United Nations human rights office voiced serious concern at the “apparent enforced disappearance” of Khashoggi and called for the two countries to investigate.

“If reports of his death and the extraordinary circumstances leading up to are true, this is truly shocking,” UN human rights spokeswoman Ravina Shamdasani told reporters in Geneva.

Senior officials in Ankara are convinced Khashoggi was killed by a Saudi state hit squad sent to Istanbul to abduct or kill him, who were lying in wait when he arrived at the consulate.

It was Khashoggi’s second visit to finalise his divorce, after being told the previous Friday that his papers were not in order. His fiancée, Hatice Cengiz, waited outside.

Flight records show two Saudi planes arrived at Istanbul’s Ataturk airport on Tuesday and left separately the same day, hours after Khashoggi was last seen.

Saudi authorities insist they played no role in Khashoggi’s disappearance. They acknowledge a “security delegation” was sent to Istanbul on Saturday but have not said why.

Turkish investigators have hinted they know more about the disappearance than they have said. Though wary of each other, Saudi Arabia and Turkey have traditionally tried to avoid public rows.

The countries have significant trade and investment ties and vie for influence across the region.

Erdogan’s response is likely to become more pointed in the coming days if there is no movement on issues that matter more to him than the disappearance of a foreign national inside Turkey.

Khashoggi has been one of Crown Prince Mohammed bin Salman’s most prominent critics.

A member of the Saudi elite, he had remained in exile in the US for much of the past year, from where he wrote columns for The Washington Post criticising aspects of the Kingdom’s reform programme.

Turan Kislakci, a friend of Khashoggi, said the 59-year-old told him he had been invited to return to Riyadh by the crown prince to act as an adviser.

Khashoggi had sought assurances about his safety from friends in the US before visiting the consulate and had asked Cengiz to contact Turkish authorities if he failed to emerge.

She raised the alarm four hours later, by which time the convoy is believed to have left.

On Tuesday The Washington Post published a surveillance image showing Khashoggi walking into the consulate, just before he disappeared. The image bore a date and date stamp and The Post said “a person close to the investigation” shared the image with them.

Khashoggi’s disappearance has shocked many in Turkey.

Calls for clarity from the international community have also mounted, with Britain and France seeking explanations from Riyadh.

Speaking for the first time about the allegations, a UK Foreign Office spokesman said: “These are extremely serious allegations. We are aware of the latest reports and are working urgently to establish the facts, including with the government of Saudi Arabia.”

France said it was seeking an explanation as to how an “accomplished and esteemed” journalist had vanished.

And US President Donald Trump told reporters he was “concerned” about “some pretty bad stories” about Khashoggi’s fate. On Tuesday he said he would speak with Saudi officials at some point about the matter.

A top Senate ally of Trump warned of a “devastating” impact on the US alliance with Saudi Arabia if allegations are confirmed.

Republican Senator Lindsey Graham said Riyadh must provide “honest answers” to the claims that he was murdered.